A Light Emitting Diode (LED) is a display and lighting technology which is widely used in electrical and electronic products on the market as LEDs use less power, have longer lifetimes and produce little heat as compared to traditional incandescent light bulbs, and emit colored light. After assembly of an LED, each LED is tested to determine its optical and electrical properties before being sorted according to its determined characteristics. Since the characteristics of the assembled LEDs vary widely, an elaborate sorting system is used to classify and separate them after assembly.
In conventional testing and sorting systems for LEDs, the LEDs are loaded onto the testing system from an onloader such as a bowl feeder or a wafer frame. Characterization of LEDs is carried out by conducting tests such as optical and electrical tests. After testing, the LEDs are sorted in an offloader which can be in form of a bin box or a wafer frame. When wafer frames are used as onloaders or offloaders, the testing and sorting of LEDs typically constitute separate testing and sorting systems. LEDs on an onloader wafer frame are conveyed to a testing system for testing. After testing, LEDs are loaded onto an output wafer frame according to a Cartesian or xy coordinate test map on the output wafer frame. FIG. 1 is an isometric view of a wafer frame 100 of a conventional LED testing system for receiving LEDs wherein the LEDs are mapped according to an exemplary Cartesian coordinate test map 102. The wafer frames loaded with tested LEDs are stacked in a magazine. Each loaded wafer frame is transferred from the magazine to a sorting system for the LEDs to be sorted according to a given Cartesian test map before being offloaded onto designated output wafer frames, each of which is identified with a desired binning characteristic. The number of output binning characteristics that are sortable is usually limited by the number of wafer frame magazines contained in the offloader.
In a conventional sorting system, only one LED can be offloaded at a time and only one offloading station is practical. As there is only one offloading station, once all the LEDs with desired characteristics are loaded onto a designated output wafer frame, the sorting process must be halted so that the output wafer frame can be removed and another designated output wafer frame such as one with a different binning characteristic is positioned before sorting continues. This introduces wafer exchange time wherein the sorting process is halted, and such idling time of the LED sorting system results in reduced throughput when sorting LEDs. It would therefore be desirable for sorting operations to be allowed to continue on an output wafer frame while a previous output wafer frame is being removed.